Vision is a complex phenomenon that involves different stages, all closely interrelated. In a first stage the images of the objects that comprise the scene that surrounds the subject is formed on his retina, an organ located at the back of the eye. Afterwards, in a different stage, the retina converts the images into electric impulses and physical-chemical signals that are sent to the brain by means of specialized neurons. The last level of the process occurs in the brain, which is where the interpretation of the image is produced through diverse psychological processes that lead to the final perception of the objects that initially provoked the visual phenomenon. In the first stage, commonly referred to as the optical stage, the quality of the images produced on the retina is received through the aberrations that the optics of the eye introduce, this being understood as an image forming system. Thus the interest in measuring and correcting aberrations in the eye is basic in the context of vision. In human beings vision is binocular, carried out through the cooperation of both eyes. This implies a series of improvements and advantageous characteristics in relation to the end perception of the object with respect to the monocular case, in which vision is carried out through a single eye.
The objective measurement of aberrations of the wavefront and their correction by means of adaptive optics, understood as compensation in real time, has been described in the case of the human eye from the beginnings of the XXI century. Thus the work of E. J. Fernández, I. Iglesias, and P. Artal, “Closed-loop adaptive optics in the human eye”, Opt. Lett., 26, 746-748 (2001) contains a first practical implementation of an experimental measurement system using a Hartman-Shack type wavefront system and an electrostatic deformable membrane mirror to obtain compensations of aberrations of the eye in real time. Out of all of the existing means for wavefront measurement, nowadays the Hartmann-Shack sensor is the most used in the context of the optics of the eye. It was originally introduced in the works of J. Liang, B. Grimm, S. Goelz, and J. F. Bille, “Objective measurement of WA's of the human eye with the use of a Hartmann-Shack wave-front sensor,” J. Opt. Soc. Am. A 11, 1949-1957 (1994); J. Liang and D. R. Williams, “Aberrations and retinal image quality of the normal human eye,” J. Opt. Soc. Am. A 14, 2873-2883 (1997); as well as P. M. Prieto, F. Vargas-Martin, S. Goelz, P. Artal, “Analysis of the performance of the Hartmann-Shack sensor in the human eye”, J. Opt. Soc. Am. A, 17, 1388-1398 (2000). Since then it has been employed intensively in the field of ophthalmic optics.
One application of adaptive optics of great practical interest is its use in visual simulators. The concept was originally described in the article of E. J. Fernández, S. Manzanera, P. Piers, P. Artal, “Adaptive optics visual simulator”, J. Refrac. Surgery, 18, S634-S638 (2002). The application is based on emulating some established optical conditions in a controlled manner and recording the perception of the subject to some stimuli or given visual tasks. In this way valuable information is obtained regarding the relation between optical quality, in terms of the aberrations, and visual quality.
New effects related to the above concept have been obtained recently, such as those shown in the article P. Artal, L. Chen, E. J. Fernández, B. Singer, S. Manzanera, D. R. Williams, “Neural compensation for the eye's optical aberrations”, J. Vis., 4, 281-287 (2004). The concept of visual stimulation by means of adaptive optics has also been successfully demonstrated for purposes of designing ophthalmic elements.
Specific examples applied to intraocular lenses and contact lenses are found in P. A. Piers, E. J. Fernández, S. Manzanera, S. Norrby, P. Artal, “Adaptive optics simulation of intraocular lenses with modified spherical aberration”, Invest. Ophthalmol. Vis. Sci., 45, 4601-4610 (2004) and S. Manzanera, P. M. Prieto, D. B. Ayala, J. M. Lindacher, P. Artal, “Liquid crystal Adaptive Optics Visual Simulator: Application to testing and design of ophthalmic optical elements”, Opt. Express, 15, 16177-16188 (2007).
Different patents have likewise disclosed the use of adaptive optics in the study and characterization of vision and, more specifically, in the analysis of optical aberrations of the eye. The measurement of aberrations has been used for their subsequent correction by means of deformable mirrors or phase modulators, analysis of the refraction in the eye and its subsequent compensation with ophthalmic, contact, or intraocular lenses, and low level methods of correction in general. Thus Document U.S. Pat. No. 6,155,684 discloses a method for subjective measurement of aberrations of the eye and their subsequent or simultaneous compensation. The invention makes possible to estimate the refractive error in the eye and, consequently, the required prescription for correcting it. This method can only be used under monocular vision.
Another example is found in Document U.S. Pat. No. 6,379,005 B1, which discloses an adaptive optical system specifically for use in the human eye. This includes a measurement of aberrations of the eye by means of a Hartmann-Shack sensor and its subsequent correction by means of a deformable mirror. The procedure is proposed for the prescription of ophthalmic and intraocular lenses, and even for refractive surgery. The instrument can only be applied to a single eye. Its extension to the binocular case requires a duplication of each and every one of its components.
Along the same lines Document U.S. Pat. No. 6,722,767 B2 discloses a method that combines adaptive optics by means of a corrector element that introduces aberrations in a controlled manner, with the subjective response of the subject to the degradation of visual stimulation presented—all of this under monocular conditions. Its employment in binocular vision requires replicating the experimental system that implements the described method.
Document U.S. Pat. No. 6,709,108 describes a method for objective measurement of aberrations of the eye and its subsequent optical compensation by means of an initial correction of the focus and another additional correction of the rest of the aberrations. The method enables prescribing ordinary low level ophthalmic prescriptions such as eyeglasses and contact lenses under monocular conditions.
Document U.S. Pat. No. 6,964,480 B2 discloses a design that allows compensating aberrations of the eye in two clearly distinct steps after the aberrations have been measured by the instrument itself, or estimated by any other method. In a first step the defocus is compensated, leaving the rest of the high order aberrations to be corrected by a deformable mirror. The assembly can only be applied to one eye at a time.
Exploiting a similar concept, Document U.S. Pat. No. 7,128,416 B2 discloses a method and instrument for implementing it, capable of estimating the refraction based on objective measurements of aberrations of the eye and modifying said aberrations by means of adaptive optics. This is carried out under strictly monocular conditions.
Later in time Document U.S. Pat. No. 7,195,354 B2 was published, in which a method is proposed, together with its corresponding practical embodiment in the form of an electro-optic system that allows measuring the aberrations of the eye so as to compensate them by means of a correction device, which enables the subject to have simultaneous vision of visual stimuli. In this way a method is provided for enabling the subject to see through a corrected optic. The manner in which said invention is disclosed makes clear that the method only works under monocular vision. Thus its possible application under binocular vision requires duplicating the entire experimental system.
Other alternative methods for the correction of the wavefront by means of adaptive optics in the context of visual and ophthalmic optics have recently been proposed, as it can be seen in U.S. Pat. No. 7,350,920 B2, which applies new designs for implementing objective measurements of aberrations of the eye and their correction. The invention per se is only applicable under monocular vision.
In the current state of the art, as shown in the patents described above, one constant is the use of adaptive optics under exclusively monocular conditions. However, the vision of human beings is obviously binocular, and the interaction of both eyes in the final perception of the images is basic. Consequently, in the context of vision the above methods only provide a partial solution to the problem of assessing optical quality and its correction. Thus the result is that for the possible application of all of the methods known to date in binocular conditions, it is necessary to duplicate the experimental systems. This entails increasing the complexity of the electro-optical systems and increasing costs, which in practice makes simultaneous use in both eyes unreasonable. The invention disclosed in this document resolves this basic problem, enabling the measurement and compensation, and in general the manipulation, of aberrations of the eyes in a binocular manner employing a single aberration correction device and a single sensor of aberrations. Furthermore, the method provides a way of showing visual stimuli in a manner simultaneous with the operation of the rest of the system.